Door construction



May 15, 1951 N. MICHELMAN 2,552,992

nooR CONSTRUCTION Filed May 28, 1947 5 Sheets-Sheet 1 IN V EN TOR.

N. MICHELMAN DOOR CONSTRUCTION 5 Sheets-Sheet 2 INVENTOR.

H IIIJIJIIIEIJLIIIIIEIELIIIIIUhIn/l 1 May 15, 1951 Filed May 28, 1947 Maly 15, 1951 N. MICHELMAN 2,552,992

noon coNsTRuc'rIoN Filed May 28. 1947 5 sheets-sheet s IN V EN TOR.

May 15, 1951 N. MlcHELMAN DOOR CONSTRUCTION T9111 l www 1 HMH TM v5 Sheets-Sheet 4 Filed May 28, 19.47

May 15,1951

N. MICHELMAN DOOR CONSTRUCTION 5 Sheets-Sheet 5 Filed May 28, 1947 WHR/mf.

INVENTOR.

BY v j@ l Patented May 15, 1951 UNITED STATES PATENT OFFICE DOOR CONSTRUCTION Nathan Michelman, New York, N. Y.

Application May 28, 1947, Serial No. 751,076

9 Claims. (Cl. 1GO-189) This invention relates generally to closures employed in building constructions and is particularly directed to a novel and improved construction of a door of the type adapted to be elevated and swung to an open position, as used in wharves, warehouses, and other industrial buildings, to afford access to loading platforms and storage space. This preferred use of my invention, with reference to which the invention will be particularly described and illustrated, is set forth solely by way of example, and it is to be understood that the invention itself is susceptible of a considerable range of applications in a nurnber of constructions other than those hereinbefore specifically listed.

Doors of the character of that forming the subject matter of this invention are usually made in such a way as not to interfere with the loading operations which must be carried out through the doorway, and at the same time to save headroom, since this latter is naturally sharply limited in the usual warehouse or wharf constructions. To this end the doors are usually made in sections, for instance an upper and a lower section, and means are provided for swinging both sections to an overlapping substantially horizontal position out of the door way, leaving the same free for the loading operations. A number of doors embodying such general characteristics are known in the art, and in some of them the sections are first overlapped, and then swung to the horizontal. This invention is advantageously applied to doors of such a type. It is to be considered that doors of this type must be easily maneuverable from a closed to an open position and vice versa, without waste of time and without the application of an excessive effort, and it is necessary therefore that their operation be as quick, smooth, safe, and even as possible. Furthermore, the doors must be completely stable in their closed position and must not be capable of opening even partially by accident, for instance, when struck by a ygust of wind. In order to render the operation of the doors easy, they are usually provided with counterweights. The ideal counterweight would have the same weight as the door or section thereof which it is intended to balance, or at least a weight equivalent thereto when referred to a cable or chain transmission interposed between the counterweight and door or section thereof. It is however understandablethat, especially in the case of a sectional door and one which is/ swung from a vertical to a horizontal position in the course of the opening operation, the effective weight of the door or door section to be overcome during the various stages of said opening operation does not remain constant. The precise relationship between the effective weights and the counterweights during the various phases of raising a section door of the type herein disclosed and claimed, will be set forth fully later on. However it is pointed out at this stage that Ithe problem of fitting the operation of the counterweight to the changes of the effective door weight of the door to be balanced has been lgiven considerable attention in the art but, as far as I am aware, has not satisfactorily been solved.

.Accordingly, the general purpose of this invention is to provide a door construction the operation of which will be easy and smooth at all times and wherein there will always be perfect balance between weight and counterweight.

A more specific purpose is to provide a sectional door construction wherein the same counterweight is made to counterbalance at the start of the operation the weight of the lower section, and at a subsequent stage the weight of both sections, and in the last stage a part of the weight of both sections.

Another purpose is to provide an operating mechanism for a sectional door wherein the connection of the counterweightto the two door sections varies automatically during the opening and closing of the door to provide at all timesV perfect balance between weight and counter- Weight and thus minimize manual effort.

A further object is to provide a sectional door construction of the type wherein the lower section is first raised to become substantially juxtaposed to the upper section, and then both sections swing from a vertical to a horizontal position being guided at one end thereof by substantially horizontal tracks, which door construction fully achieves the purposes hereinbefore set forth.

A still further object is to provide in a sectional door construction achieving the foregoing ob-A ject, an operating mechanism comprising one or' more counterweights and sheave and chaini means connecting each counterweight to each section of the door, the connections to the lower door section being operative at all times and the connections tothe upper door section becoming automatically operative at the beginning of a certain predetermined stage of the door-raising operation and returning automatically to an inoperative condition at the end of such stage,

said connection becoming operative for a like perod of4 time during the door lowering operation.

A still further object is to provide in a sectional door construction an operating mechanism achieving the foregoing object, wherein the period of time during which the connections of the counterweight cr counterweights to the upper door section are operative, may be adjusted to t the optimum requirement of the particular door to which the mechanism is applied.

Other related and ancillary objects ofv my invention will clearly appear as the description proceeds.

In the drawings: l

Fig. 1 is an elevation of a door according to this invention viewed from the inside of the'bililding structure to which it is applied.

Fig. 2 is a vertical cross-section "takenon the line 2-2 of Fig. l looking in theidirection-lofsthe raised it will carry therewith the upper section. Both door sections are actually suspended from two operating units located at each end of the door, and which will be described in detail hereinafter. The two operating units are connected by a shaft I4 which is disclosed in the drawings as a metal pipe journalled in a number of supports l5, conveniently attached to the building structureto which the doorfis-applied `and close enough 'together f'suiiiciently to reduce the free spans of the shaft I4. The two operating units .aforementioned are symmetric and mechanically identical except in that the right hand side unit,

f vafs'i'ifiewed'in Fig. 1, embodies a hand chain wheel arrows, with part of the lower door sectionbroken trating=atan enlarged s'calethe sheaves V'andassoc'iated'operative'mechanism. 'Y ff-Figgi is lan elevation'and' partial section 'o'ffthe assembly of Fig. B'tak'en onthebrokenlin'eA-d of Fig. 3 looking in the direction 'of 'the' arrows.

VFigl fan elevation,rpartly broken, of 'the counterweightand as'sociated'sprocket. y Fig. 6 is a'plan viewof Figf'. Fig.' 7i's a plan 4view :andFigJB 'is 'an elevation ofa dtail of .a modiedembodiment ofthe invention." Figs. 9, 10, l1 and 12 are schematic `perspectiife viewsl cfa lportion'of'the doorsect'ions and operativemeohanism" illustrating the 1farious' phases-'ef the operationofsaid'mechanisrnandFigs.'-9a,li0a; 11a: and 112a`a`r`e fscl'iernatic4 elevationsiof a detail of themechanism seen'inthe same `phases of theoperation; Y

a's-fshownfinFigi consists 'of two sections,v an upper-section fIU and ra lower'section II. Thel'deta'ils'ofthefd'oor 'sections are of course' matters of judicious `'design and areinotpertinentfinsofar as this invention is concerned; therefore lthey are-not illustrated infthe-'drawings The 'said door sections mayvconprise a'numb'e'r of 'panelsfas indicated somewhatsch'ematioally `in Fig. lfan'dglass pa'nelsmaybe embodied therein, as desiredlin eaohfindividuaiinstance. area'pproximate'ly of theV same weight, but 'the door section `Ill is 'preferably slightly'heavier for instance'byfabout 20% "than the'lower section VII. Nevertheless in discussing the roperationfof"the counterweights :this diierence in weightb'etween theV ftwb `-sections will `be` sometimes 'disregarded because lit is Yto lbe understoodthatinthe motionsv of la door of this "type there is involved :a certain degree of vfriction `Vso thatlthe counterbalancing need not be Vrigorously exact fandflmoderate differences in weight will be absorbed-by the friction of the moving 'parts 'without -in'terferingwith the satisfactory operation ofthe door mechanism. `'At any rate, the upperfsection fI hasverticalf guides provided therein. fas indicated forvnstancefinFig. 2 atfIZ, for guidingthe lower sectionfII in its Vertical mo'tionparallel to 'the upper section and fori'maintaining thertwos'ecti'onstogether as a unit vwhen they overlapeach other. rFurther' the upper/door section I (Vhas'a plate I`3"attach'ed to the upper portion thereof,

sectionp'so that if the lower section-'isulthelf The tw'o door sections f meshingwitha hand chain by which the door is "operatedl For 'this reason only the right hand 'side -unit will Y'be-described and illustrated in detail.

With-"particular reference to Figs. 2, 3 and 4, said right hand side operating unit comprises a supporting frame generallyindicated atA I6 which is-s'ecufed in any convenient manner to the building fst'ruo'ture. Said frame I6 comprises a'pla'te` I1,'la T-be'am I8 'having certain-cut-out portions asfshown in the drawings and being weldedto the plate: |11, 'and'another plate I9 weldedto thebearnV I8. 'Tosecure'the frame in fplace, 'the `plate-I1 maybe a't'tached'to `thefa'cia plate 5I=in any con# venient "manner, las for instancel by vmeans of arigle2ll,fand the beam I8 may be'a'ttached to an'gle2I rigidly connected to `-said lfacia pla-te. The-plates I 11` and I 9 provide journals f for a Vshaft 22,' Asaid journalsbeingv preferably provided with ball bearings: or thelike, laridsaid shaft 22 is con-v nected by means of a iiexible coupling 2`3'to the shaft aforesaid Keyed-to thefshaftv22 to the outside of 'the frame' IB-is a sheave 24. Anothersheave V25 `isfidle 'on the shaftv22 and is positioned'- between the plates -I1and I9. Both sheaves are conveniently lsecured against axial displacement;l The sheave 25 has attached thereto 'a pin 26` which is long enough-tov come in contact with the plate I9 invfcertain'po'sitions of the sheave-'25. For purposes which `Wil1 be" set forth hereinafter,

' two slots 21 and 28 are' usually formed in the plate I9' in-l'su'ch a position that the pin 26 `may enter -A 'cover' 29 is attachedV to the platel I1 and forms therewith a gearbox=which is-normally filled with grease. 'Said gear boxand the elementshereinafter-t0 be described'are not present'in the lefthandfside unit. Within'thefgear b'ox the shaft 22-has keyed theretoa gear 530 meshing withia gear 23| keyed toa `spindle 32 -journalled iii-*the ;plate I1.andlinthe cover 29. Another gear N33'is keyed'to the spindle jl$2 and meshes-with a gear 34A keyedfto a shaft35 .which supported inthe platel1 andin a hub member 3'6 attached to said plate I1.v The shaft 35 has also keyed thereto a hand chain wheel 31 meshing withfa chain f-38 (said chain .has Vrbeen fomittediin iFig. f3). f The above described gearing vconnections operate 'to rotate the'shaft'22 and therefore thelfshea've 24 whenlthe handchainwheel 31 is rotated-by@ pullinglthe chain38in one or theother directionand to multiply the torque manually appliedtofsaid wheel 31. Y

Acounterweght39 is positioned as indicated in yFig. 2 below the sheaves 24 and 25 randis yguided forvertical"reciprocationdn any suitable manner in the'buildingstructure or in guides. xed thereto. Brackets 4I] are attached t'o vthe topof ythe counterweight 39Y and rotatably "carry alsprocket 4I. Achain 42 connects the :two sheaves and the sprocket of lthe counterweight in the following manner. One end of the chain 42 is connected to a rollor 43 attached to the lower end of the lower door section Il. The chain 42 then meshes with the keyed sheave 24, subsequently with the sprocket 4I of the counterweight, and subsequently with the idle sheave 25, and finally is attached at its other end to a point 44 located intermediate the upper and lower end oi' the upper door section i9. These connections will be well understood by reference to schematic Figures 9 to 12.

The mechanism is completed by a track 45 which is attached by means of hangers 45 to a part of the building structure, in the example illustrated to the roof structure 4?. The first part of the track 45, indicated at 48 is curved, for reasons that will be hereinafter set forth. The track 45 is adapted to be engaged by a follower roller 49 mounted on a bracket 5i! attached near the upper end of the door section lll.

The operation of the door mechanism will be best understood with reference to schematic Figures 9, and 9a to 12, 12a, wherein 9a illustrates the position of the idle sheave when the whole mechanism is as in Fig. 9, and so on. It is understood that there actually are two counterweights as there are two operating mechanisms, which are connected for synchronic motion by means of the shaft Hi. Therefore in the following when the expression counterweight is used` it is to be understood as embracing both counterweights and likewise the expression keyed sheave, idle sheave, pin, and the like are to be understood as embracing both corresponding elements in the two operating units. Only the hand chain wheel 31 and associated mechanism are present in one unit, in this particular case the right hand side unit (although it could be the left hand side unit as well) and not in the other. The schematic Figures 9, 9a to 12, 12a actually show the left hand side unit, and therefore the hand chain wheel is not represented thereon. The numerals designating therein the various parts are the same as those designating corresponding parts in the right hand side unit, except in that the letter a is aiiixed thereto.

When the door is closed, the operating mechanism is in the position of Fig. `9 and the sheave 25a is in the position of Fig. 9a, with its pin 26a all the way in the slot 2id. Itis seen that the door cannot accidentally become displaced from that position because of the action of wind, due to the fact that the initial portion 48 of the track 45 is inclined. The counterweight 39a is in its uppermost position. If now the hand chain 38 is operated to open the door, the shaft 22, and therefore the shafts lli and 22a, rotate and so does the keyed sheave 2da. As a result the lower section El of the door is raised sliding in engagement with the guides l2 provided in the upper section. This latter remains in position so that the end lilla of the chain 42a is actually a dead end and the idle sheave 25a does not move. This operation is facilitated by the fact that the upper section is somewhat heavier than the lower section. The counterweight 39a descends, but in view of the connections of the chain 42a hereinbefore described, it only descends at half the speed at which the lower section Il rises, and therefore only half of the weight thereof is effective. Since the two counterweights 39, 39a together are approximately twice as heavy as either section of the door taken singly, a satisfactory balance is maintained during this phase of the operation. At the end of the first phase of the operation the position of Figs. 10 and 10a is attained, and the two door sectionshave-reachedl an overlapping positioned relationship. ,Ifnow the hand chain 38 is further actuated, the top of the lower section l I engages the plate I3` and the two door sections move together as one unit, guided in theirmotion by the engagement of the rollers 49 with the tracks 45. It is apparent therefore that at this point the entire weight of the door must be counterbalanced, and this end is achieved because the point 44a ceases to be a dead center and becomes a live center as the upper section I0 also rises. The idle sheave 25a begins to rotate in a counterclockwise direction,l carrying with it the pin 26a, and the speedof descent of the counterweight is incr-eased. Thus the entire weight of both counterweights is made effective and a satisfactory balance is maintained in the second phase of the operation. At the end of the second phase, the positions of Figs. 1l and lla. has been reached and it is seen that the two door sections are slanted at an angle which is shown herein as about 45, but need not necessarily have such a value. Because of this slant of the door sections, a portion of their weight is borne by the tracks 45 and if the entire weight of the counterweights were still effectiveit would exceed considerably the amount required for balancing the door. Therefore the motion of the door would go out of hand and would have to be manually restrained. However when the position of Figs. l1 and 11a has'beenY reached', the pin 26a fixed to the idle sheave 25a has penetrated into the slot 28a of the plate l9a and has reached the end of that slot. It is therefore prevented from going further, and the idle sheave 25a is prevented from rotating any further. So the part of the chain 42a which mesheswith said sheave becomes again a dead center, the speed.

of descent of the counterweight is slowed down,

and once again, as in the first phase of the operation, only half of the weight of the counterweights is effective. A satisfactory balance is therefore maintained during the last phase of the operation at the end of which both door sections are horizontal and lie in the position indicated at Fig. 12. It is noted that in this position the portion of the chain 42a which runs from the idle sheave 25a to the point la of attachment of the chain to the upper section l!) is slack as indicated, in a somewhat exaggerated manner, at 52a in Fig. l2. If now the hand chain 38.is operated to lower the door, the above mentioned motions take place in reverse order. First, from the position of Fig. 12 to that of Fig. 1l, only the keyed sheave rotates, the slack in portion 52a of the chain is taken up, and therefore the-idle sheave 25a does not rotate. Thus only half of the weight of the counterweights is effective. When the position of Figs. l1 and 11a is reached, the portion Y.

52a of the chain has become taut, therefore as the door continues to be lowered it forces the idle sheave 25a to rotate in a clockwise direction, accelerating the rising of the counterweight and making the entire weight thereof effective. This takes place until the position of Figs. 10 and 10a is reached. Therein the pin 26a fixed to the idle sheave 25a has engaged the slot 21a in the plate ld, and has reached the end of said slot, so that the idle sheave must stop, yand the portion of the chain meshing therewith becomes again av dead center. Half of the counterweights is only effective from this point on, and the upper section of the door remains inplace, while the Alower Y directrice sectione'lone moves vertically downwardsfto vthe completely closed' 'position'. of 'the door.

, Itismseenjfrom jtvlie above that the length of "during which the entire lweight of the counterweights iseective'depends on the angle byjwhich' the idle sheaves are allowed to rotate. This angle', with reference to the particular embodimentudescribed so far depends upon the anglesubtended by the ends of the slots 21 and 28,21a andv 28a. I have foundthat the optimum periodI of effectiveness of the entire weight of the counterweights may vary from case to case, depending uponv the weight and characteristics of the' particular door to which the mechanism is applied. Therefore the aforementioned angle is a-'matter ofjjudicious' design. Accordingly slots 2] and 28, 21a and 28a have to be cut more or le's's deep. In view of the desirability of eiecting this adjustment in a simpler and more convenient way, an alternative embodiment of this invention is illustrated in Figs. '7 and 8 in which there'- isv shown simply avplate 53 designed to take the place of the plate i9 in the assembly here- 'inbefore described. This plate 53 is so positioned inthe assembly that it will not be contacted directly by the pin fixed to the idle sheave, but it .has attached thereto facing the idlesheave two 4blocks 54'and 55, each of which is female threaded -to` receive a bolt 56 and 51 respectively. The pin 25' of the idle sheave will contact the boit 5% in the position of Fig. lOaiid the bolt l in the position of'Fig. 1l to achieve the operation hereinbeforedescribede -Thetwo end portions of the pin A26 are shown in phantom lines in Figs. -7 and 8. It is clear that Aby screwing the bolts 55 and' '51 in and out of the respective blocks, the anglefof rotation of the idle sheave can be increased or diminished as desired, and therefore the period in which the entire weight of the counterweight is effective can be controlled without lthe need of any structural changes in any parts of the device.

In the foregoing there has vbeen .described preferred manners of carrying out the invention. It is to be understood however that many changes may be'made in the configuration of the various parts of the mechanism and their respective arrangement. Particularly, the invention contemplates the provision of elements respectively fixed to the idle sheave and to the frame on which the operating mechanism is mounted, said elements beingadapted to engage each other to stop the rotation of the idle sheave at a predetermined stage ofthe operation of the mechanism. The element fixed to the sheave has been described as a pin,.but it could of course assume any other suitable shape, and the element fixed to the frame has beendescribed either as a notched plate or as a bolt, but could likewise be of different structure, as long as the elements are adapted to engage -each other to Vachieve the motion limiting function set forth hereinbefore. Therefore many changes, variations or adaptations could be made in the device by persons skilled in the art without'departing' from the spirit of the invention or exceeding the scope of the claims.

I claim:

`Vl. An operating mechanism for a door embodying a lower and an upper section, comprising a shaft, Va sheave keyed thereto, another sheavefreely mountedthereon, .counterweighting means Aattached to a sprocket, a chain attached at one end to the lower door section, successively meshing .with said keyed sheave, said sprocket, andl said free sheave, rand finally attached 'at its 8:' other end to the .upper-door section, Vwhereby said sprocket is supported by a` middle' portion of said chain interposed'between said two`sheaves and the full weight of said counterweighting means is effective only when both sheaves rotate with said shaft, meansV for rotating said shaft to open and to close the door, a projection on said free sheave and means positioned in the path of movement of said Vprojection and engageable thereby during the rotation of said free sheave for limiting the rotation of said free sheave and, therefore, the time during which the full weight of such counterweighting means is effective.

2. An operating mechanism for a door embodying a lower and an upper section, comprising a frame xed to thek building structure to which the door is applied-a shaft journalled in said frame, a sheave keyed thereto, another sheave freely mounted thereon, counterweighting means attached to a sprocket, a chain attached at one end thereof to the bottom of the lower door section successively meshing with said keyed sheave, said sprocket, and said free sheave, and finally attached at the other end thereof to an intermediate portion of the upper door section, whereby said sprocket is supported by a middle por-r tion of said chain interposed between said two sheaves and the full weight of said counterweighting means is effective only when both sheaves rotate with said shaft, a stop member xed to said free sheave, means carried by said frame and engageable by said stop member to limit the rotation of said free sheave in either direction, to limit the period during which the full weight of said counterweighting means isv effective, and means yfor rotating said shaft to open and close the door.

3. An operating mechanism for a door embodying a lower and an upper section, comprising a frame xed to the building structureto which the door is applied, a shaft journalled in said frame, a sheave keyed thereto, another sheave freely mounted thereon, counterweighting means attached to a sprocket, a chain attached at one end thereof to the lower door section, successively meshing with said keyed sheave, said sprocket, and said free sheave, and nally attached at the other end thereof to the upper door section whereby said sprocket is supported by a middle portion of said chain interposed between said two sheaves and the full weight of said counterweighting means is effective only when both sheaves rotate with said shaft, means for rotating said shaft to open and close the door, a projection on said free sheave and means positioned in the path of movement of said projection and engageable thereby during the rotation of said free sheave for comining the rotation of said free sheave to a predetermined angle, and means for displacing said last-named'm'eans to vadjust the position thereof relative to the path of movement of said projection, whereby to vary the aforesaid angle of rotation of the free sheave and, therefore, the period during which the full weight of such counterweighting means is effective.

4. An operating mechanism for a door embodying a lower andan upper section, comprising a frame fixed to the building structure to which the Ydoor is applied, a shaft journalled in said frame, a sheave keyed thereto, another .sheave freely mounted thereon,counterweighting means attachedto a sprocket, a chainattached at one end to the lower door sectionsuccessively meshing ivith'saidk'eyed sheave, said sprocket, andv 9 said free sheave, and finally attached at the other end to the upper door section, whereby said sprocket is supported by a middle portion of said chain interposed between said two sheaves and the full weight of said counterweighting means is effective only when both sheaves rotate with said shaft, a projection fixed to said free sheave, means engageable by said projection to limit the angle of rotation of said free sheave in either direction, said means being adjustably positioned on said frame relative to the path of movement of said projection, whereby the angle of rotation of said free sheave may be varied and, therefore, the period varied during which the full weight of said counterweighting means is effective, and means for rotating said shaft to open and close the door.

5. In combination with a door embodying a lower and an upper section, said door being openable by sliding said lower section vertically to a partially open position wherein the same is in overlapping relationship to the upper section and by swinging both sections therefrom to an open position wherein they are in substantially horizontal and superimposed ,positioned relationship, said door being closable by reversing themotions aforesaid, an operating mechanism for the door comprising a shaft, a sheave keyed thereto, another sheave freely mounted thereon, counterweighting means attached to a sprocket, a chain attached at one end to the lower door section, successively meshing with said keyed sheave, said sprocket, and said free sheave, and finally attached at its other end to the upper door section whereby said sprocket is supported by a middle portion of said chain interposed between said two sheaves and the full weight of the counterweighting means is effective only when both sheaves rotate with said shaft, means for rotating said shaft to open and close the door, a projection on said free sheave and means mounted in the path of movement of said projection and engageable thereby during the rotation of said free sheave, for stopping the rotation of said free sheave in the opening of the door when both sections in their aforementioned swinging motion have attained a predetermined angle, and further means mounted in the path of rotation of said projection in spaced relationship to said first-named means, and engageable by said projection during the rotation of said free sheave for stopping the rotation of said free sheave when said partially open position has been attained.

6. In combination with a door embodying a lower and upper section, 'said door being openable by sliding said lower section vertically to a partially open position wherein the same is in overlapping relationship to the upper section and by swinging both sections therefrom to an open position wherein they are in substantially horizontal and superimposed positioned relationship, said door being closable by reversing the motions aforesaid, an operating mechanism for the door comprising a shaft, a sheave keyed thereto, another sheave freely mounted thereon, counterweighting means attached to a sprocket, a chain attached at one end to the lower door section, successively meshing with said keyed sheave, said sprocket, and said free sheave, and finally attached at its other end to the upper door section, whereby said sprocket is supported by a middle portion of said chain interposed between said two sheaves and the full weight of the counterweighting means is effective only 10 when both sheaves rotate with said shaft, means for rotating said shaft to open and close the door, a projection rigid with said free sheave and means engageable by said projection for stopping the rotation of said free sheave in the opening of the door when both sections in their aforementioned swinging motion have reached a predetermined angle, and means engageable by said projection for stopping the rotation of said free sheave in the closing of the door when said partially open position has been reached.

7 An operating mechanism for a door embodying a lower and an upper section, comprising a frame xed to the building structure to which the door is applied, arshaft journalled in said frame, a sheave keyed thereto, another sheave freely mounted thereon, counterweighting means attached to a sprocket, a chain attached at one end thereof to the bottom of the lower door section, successively meshing with said keyed sheave, said sprocket, and said free sheave, and finally attached at the other end thereof to an intermediatevportion of the upper doorsection, whereby said sprocket is supported by a middle portion of said chain interposed between said two sheaves andV the fullr weight of said counterweighting means is effective only when both sheaves rotate with said shaft, a projection fixed to said sheave, two members fixed to said frame, a bolt engaging each member so positioned that the head thereof is engaged by said projection to stop the rotation of said sheave in a predetermined angular position thereof, the angle by which said free sheave is allowed to rotate between said two engaging positions of said projection being adjustable by rotating said screws, to regulate the period during which the full weight of said counterweighting means is effective, and means for rotating said shaft to open and close the door.

8. In a door construction an upper section, a lower section, means for guiding said lower section in sliding motion with respect to said upper section, means for limiting said vertical motion, track means xed to the building structure to which the door is applied and engaged by follower means mounted on said upper section, said track means embodying a substantially horizontal portion, a shaft journalled in supports fixed to the building structure, a sheave keyed to said shaft, another sheave free on said shaft, counterweighting means attached to a sprocket, a chain attached at one end to the bottom of the lower section, successively meshing with said keyed sheave, said sprocket, said free sheave, and nally attached at its other end to an inter-mediate portion of the upper section, a projection on said free sheave, Xed stop means engageable by said projection, and means for rotating said shaft in either direction, whereby when said shaft is rotated to open the door the lower section is first raised vertically to overlapping relationship to the upper section While said free sheave remains stationary, subsequently the bottom portion of both sections are raised while the top portions move guided by said follower means along said tracks and said free sheave rotates, whereby the full weight of said counterweighting means is effective, until a predetermined slanted position of the door sections is reached wherein said projection on said free sheave engages one of said stop means and the rotation of said free sheave ceases, and subsequently the motion aforementioned of the door section is continued until the same has reached a substantially horizontal position, and

Athat point said projection of the free sheave engages the other stop means' and the rotation of said free sheave is stopped.

9. An operating mechanism for a, door, comprised of an upper and lower section, embodying two units located at eachrside of the door; each unit comprising a frame fixed to the building Vstructure to which the door is applied, a shaft journalled insaid frame, a sheave keyed thereto,

; another sheave freely mounted thereon,rcounter weighting means attached to a sprocket, the combined weights of the two counterweighting means .being approximately equalto the total weight of -the door, a chain attached at one end thereof to the lower section of the door, successively meshy Y weighting means is effective only when both sheaves rotate with said-shaft, a projection on said free sheave, and stop means mounted on said frame and engageable bysaid projection to limit the rotation of said free sheave in either direction, to limit the period during which the full weight of the said counterwei'ghting means is effective to a predetermined angle, the stop vmeans and projection of the two units being in the same angular position; an intermediate Vshaft rotatably supported by the building structure and operatively connecting the shafts of the two units; Ya hand chain wheel ,keyedv to one of the aforementioned shafts, and a hand chain for operating said wheel in either direction to open and close the door.

NATI-IAN MICHELMAN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,178,945 Ritter Apr. 11, 1916 1,369,425 McHarg Feb. 22, 1921 1,646,432 Tomkinson Oct. 25, 1927 

